1. Field of the Invention
The present invention relates to a Single Inductor Double Output (SIDO) power converter and driving method thereof, more particularly, a SIDO power converter with low cross regulation and low energy loss and driving method thereof.
2. Description of the Prior Arts
The power management IC is widely used in the portable electronic products, such as mobile phones, PDAs, even notebook computers, etc., and therefore the power management is a very important and very active study topic in the electronic field. The industry always cares about how to make the battery has the longest life and the optimum efficiency so as to obtain the perfect product and enhance the product competitive abilities. The configuration of SIDO power converter is distinct from the tradition DC to DC converter and the SIDO power converter may decrease the usage of the external elements (for example, inductors) for saving cost and enhancing the product competitive abilities. By reducing the usage of the inductors, the size of the PCB board will shrink to achieve the final goal of the portable product micromation. Simultaneously, under the tendency of the system on chip (SoC), it needs to input a power source into the system for the power management module, and then provides the different voltage to the different systems or circuits according to the actual requirement and design. Thereby, in accordance with the SIDO configuration (or multiple output voltages), it merely needs to use a single power management module and the smaller external energy storage elements (for example, inductors and capacitors) to achieve the perfect power convert for obtaining a steady output voltage and a required output current and performing the more efficient use of the battery.
The prior art applies the pseudo-CMM current technology for actualizing the SIDO configuration (multiple outputs) because of the cross regulation and the system stability, for example, U.S. Patent Application 2004/0201281 A1 and IEEE J. Solid-State Circuit, Vol. 38, NO. 6, pp. 1007-1014, June, 2003. Thereby, the entire system does not have the discontinuous current mode (DCM) causing the entire system is easy to steady, and moderately solve the problem of cross regulation based on the small current (equivalent to zero inductor current of DCM). However, it needs to add freewheel section during the entire plus width modulation (PWM) period for achieving the control technology mentioned above. And in actual design and requirement, most of the power will be lost in the freewheel section because of the equivalent resistance effect of non-ideal switch, and therefore the conduction loss of the entire circuit system is increased so as to affect the energy conversion efficiency. Especially when the inductor needs to accept the higher current, the conduction loss becomes more serious (Pcon=I2Ron). Additionally, the energy stored in the inductor can not transfer to the output terminal because the freewheel section joined, and therefore the average current of the inductor is larger than the sum of the current from the loads of the output terminals. Moreover, due to the characteristic of DCM on the output terminal of the inductor in the SIDO module, the higher average current causes the higher output voltage ripper generated, and it may need a post-stage steady circuit to steady the voltage ripper. This is hardly satisfactory.
IEEE J. Solid-State Circuits, Vol. 42, No. 12. pp. 2706-2714, Dec. 2007, the prior art also discloses an energy distribution process with priority operation for achieving the SIDO (multiple output) configuration. However, this configuration only applies in certain kinds of loadings, and the output voltage controlled by the comparator in this configuration relative to the voltage controlled by the error amplifier in the closed loop, the entire load regulation (line regulation) is no good.
Accordingly, in view of the above drawbacks, the present invention provides a SIDO power converter and driving method thereof, more particularly, a SIDO power converter with low cross regulation and low energy loss and driving method thereof, which solves the drawbacks as the foregoing.